Many potentially important applications exist for two-phase heat-transfer systems whose refrigerant has, while they are not operating, saturated-vapor pressures substantially below ambient atmospheric pressure. However, prior-art embodiments of such two-phase heat-transfer systems have often been unable to compete successfully with single-phase heat-transfer systems. This is in particular true in the case of internal-combustion-engine prior-art two-phase cooling systems which have so far never been mass-produced, and have been used only in a few concept-demonstration vehicles and in a few ground installations.
I assert that a principal reason for the fact recited in the immediately preceding sentence is that most prior-art internal-combustion-engine two-phase cooling systems ingest air each time they are deactivated and their refrigerant approaches ambient air temperatures. I also assert that the prior-art describes no generally useful techniques for eliminating air ingestion from internal-combustion-engine cooling systems without    (a) constraining operating pressures to be essentially equal to the current atmospheric pressure or to differ from the current atmospheric pressure by a constant amount; or without    (b) using expensive glandless valves, and hermetically-sealed pumps, and requiring unacceptably-thick refrigerant-passage walls; and, in the case of internal-combustion engines with separate cylinder blocks and cylinder heads, without also using impractical cylinder-head gaskets.
The handicaps of prior-art internal-combustion-engine airtight two-phase cooling systems recited above under (a) and (b) apply also to many other airtight two-phase heat-transfer systems, whose refrigerant has, while they are not operating, saturated-vapor pressures substantially below ambient atmospheric pressure. Nevertheless, the prior art discloses no techniques for maintaining the internal pressure of inactive airtight two-phase heat-transfer systems above their refrigerant saturated-vapor pressure without imposing at least one of the constraints recited above under (a) and (b).
In addition to the handicaps recited above under (a) and (b), prior-art airtight two-phase heat-transfer systems in general, and internal-combustion-engine airtight two-phase cooling a systems in particular, have several additional major handicaps which must be eliminated before airtight two-phase heat-transfer systems can realize their full potential. The nature of those additional handicaps will become apparent whilst reading this DESCRIPTION.
Non-airtight two-phase heat-transfer systems do not have some of the handicaps of prior-art airtight two-phase heat-transfer systems. However, the air ingested by non-airtight systems has often been a sufficient handicap for them to be unable to compete successfully with single-phase heat-transfer systems. A prominent example where this has happened are steam building-heating systems which have been superseded by hot-water building-heating systems primarily because of the unacceptable rate of corrosion caused by air ingestion.